The present invention relates to an improved process for obtaining synthetic hides similar to natural hides by means of a chemical treatment of sheet synthetic material, and in particular by treatment of a commercially known raw material made available by KURARAY CO LTD both in its raw state and as a finished product under the name SOFRINA (registered trade mark) comprising a porous expanded polyurethane matrix in which are embedded fibres of NYLON (registered trade mark) or other types of polyamide fibres or non-woven fabric, and a covering skin made from a layer of compact polyurethane embossed in an imitation of the form of the natural hide which it is desired to imitate. More particularly the present invention relates to improvements in the similar process described in Italian Patent application No. 67585-A/84 filed on 6 June 1984 and entitled: "A process for obtaining synthetic hides similar to natural hides by a chemical treatment of sheet synthetic materials", the content of which is incorporated hereby by reference.
In the said earlier Patent application there is described a chemical treatment which surprisingly permits a porous synthetic material constituting a second rate imitation of natural leather, in that it is substantially lacking the consistency such as to give to the touch that typical sensation of natural leather, the so-called "handle" to those skilled in the art, to be transformed into a perfect imitation of natural leather almost indistinguishable by touch even to an expert; this treatment consists in subjecting a flexible porous synthetic sheet material, preferably having fibres freely embedded in the matrix and provided at the surface, on one of its faces, with a compact layer of worked plastics resin, for example stamped, in imitation of the configuration of the type of leather to be imitated, to a treatment entirely similar to the tanning treatment to which natural hide is subjected, then followed by a stuffing treatment again entirely identical to that which is performed on natural leather after tanning. The application both of the tanning treatment, which as is known serves only the purpose of making the natural collagen fibres which impart to the leather its well known properties, resistant to putrescence, and of the subsequent stuffing treatment, to a porous synthetic material which is not decomposable and which does not even have a chemical composition able to react with the substances utilised for tanning (usually metallic salts such as sulphates and chlorates) must have appeared absurd both to the tanning specialist and to the organic chemist; however, according to the process described in the above-mentioned Patent application, it is surprisingly found that the salts of the tanning solution can be precipitated within the pores of the synthetic material being treated, where they are then retained and where they subsequently contribute to the retention in a stable manner of the stuffing substances, producing a considerable increase in weight, volume and consistency of the original material, and imparting thereto, in an entirely unexpected manner, just that "handle" and the typical aspect of natural leathers. Still on the basis of the process of the above-mentioned prior Patent application, the flexibility of the starting material can be improved, even in this case approaching that of the best leather, by means of an additional "pseudo-tanning" treatment of the material before the stuffing thereof, with an aqueous solution containing a di- or polyaldehyde.
In reality, however, natural leather, depending on the type (sheep, cattle, horse, etc) of animal from which it is obtained, has different characteristics of flexibility and consistency, which in practice make one type preferable for a certain use (for example for the manufacture of soles of shoes) and another type for a different use (for example for the manufacture of shoe uppers, clothes, handbags etc); now, with the known process the subject of the said patent application it is not possible to obtain this difference in flexibility between the different types of synthetic leathers produced. In other words, starting from identical materials, but one of which, for example, has a surface configuration in imitation of calf leather, and another has a surface configuration, on the other hand, in imitation of horse leather, two final artificial hides are obtained which differ only in their external aspect but which, however, have substantially the same flexibility, unlike the respective natural leathers which they imitate.